Maybe getting published - what to charge?

Hi guys.
Received following message via Smugmug from a guy who want's to use one of my pictures:
"To Whom it may concern: My name is Jon Straumfjord. I am completing a book on a Christian subject, and I am working on the cover for first an eBook, and then a regular had-copy book. For the background of the cover, I would like to incorporate a picture of bolt lightning. When I was search the internet, I found a picture that you apparently have posted a lightning picture I would like to have your permission to use for this book (assuming you actually own the rights to this picture): xxxxxx_Sony I have attached a copy of the picture in question just in case you cannot ascertain which picture I am talking about from the information listed above. Please let me know whether you will give me permission to use this particular picture, and under what circumstances. Please send me a signed document tending your permission, or I can create one if you do not have such a document. (Please send any forwarded document as either a pdf attachment or Word Document attachment) When you respond to this email, please include the above website and picture information so I know which picture we are discussing. Thanks for your kind cooperation in this matter. Cordially, Jon V Straumfjord III President JVS3 Enterprises, contact details supplied"
I checked his contact info & it appears to be legit.
What would you suggest my reply shoud be?
No idea what to charge or how should I go about giving permission to use this photo as it is supposed to be used in an eBook, and then possibly in a regular had-copy book.
Your advice would be greatly appreciated.
Cheers.
Received following message via Smugmug from a guy who want's to use one of my pictures:
"To Whom it may concern: My name is Jon Straumfjord. I am completing a book on a Christian subject, and I am working on the cover for first an eBook, and then a regular had-copy book. For the background of the cover, I would like to incorporate a picture of bolt lightning. When I was search the internet, I found a picture that you apparently have posted a lightning picture I would like to have your permission to use for this book (assuming you actually own the rights to this picture): xxxxxx_Sony I have attached a copy of the picture in question just in case you cannot ascertain which picture I am talking about from the information listed above. Please let me know whether you will give me permission to use this particular picture, and under what circumstances. Please send me a signed document tending your permission, or I can create one if you do not have such a document. (Please send any forwarded document as either a pdf attachment or Word Document attachment) When you respond to this email, please include the above website and picture information so I know which picture we are discussing. Thanks for your kind cooperation in this matter. Cordially, Jon V Straumfjord III President JVS3 Enterprises, contact details supplied"
I checked his contact info & it appears to be legit.
What would you suggest my reply shoud be?
No idea what to charge or how should I go about giving permission to use this photo as it is supposed to be used in an eBook, and then possibly in a regular had-copy book.
Your advice would be greatly appreciated.
Cheers.